Kenwood TM-281A antenna options

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Wingnut2840

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Hello everyone. Brand new to the forum and radios in general. I'll give a little background about my situation before I ask questions. I live in WV and ride my utv (Polaris General) in some VERY rural locations. The group I ride with uses VHF radios for comms. Quite a few use the Kenwood model listed above and that's the radio I've decided to purchase as well. I want to maximize my range as best I can with the best antenna options available. We ride in some pretty round conditions though. Creeks, mud, heavy brush and trees, heavy snow etc. Most of the body is plastic, so a magnet mount antenna won't work. I'll have to chassis mount it somewhere. So.... questions:

1: Would a 6' - 8' steel whip work with these radios? What's the longest length I can use? I have a specific reason for wanting to use a whip, if possible.

2: Could I use a spring at the base of an antenna to alleviate stress on it.

3: Would a dual antenna setup improve anything?

4: What antennas would you recommend for my situation?

I'm sure these questions may sound a little juvenile. I have very little experience with radios so any knowledge or info shared would be GREATLY appreciated. Thanks in advance.

Neil
 

W9BU

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Note to forum participants thinking of joining this thread:

Answer the OP's question about his antenna choices. Don't get wrapped around the axle about how the radio is being used.

To the OP, the radio you reference is designed for the amateur radio market. You don't mention that you or the other members of your group are licensed amateur radio operators. If they are, great! The Kenwood TM-281A is not designed to be used outside the amateur radio bands. If you transmit with the radio outside the amateur radio bands, you are violating FCC rules. If you transmit in the amateur radio bands without an amateur radio license, you are violating FCC rules.
 

N4GIX

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A quarter-wave length antenna is 1.6'
A half-wave length antenna is 3.2'

Don't confuse a 27 MHz CB antenna with a 146 MHz VHF antenna. Antenna length is calculated to work with the transmit frequency, and is typically either quarter-wave or half-wave.

In brief though, the antenna you suggest would not work well at all, and is most likely to damage your radio.
 

chief21

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Considering your circumstances, it sounds like the best option for you would be a simple VHF quarter-wave whip (about 20" long). Very flexible, low-profile, and inexpensive. As you mentioned, this type of antenna does need a ground plane to operate well.

If you are not able to provide a ground plane, you would need to use a half-wave antenna instead. Half-wave antennas do not require a ground plane, but they are usually much bigger and more expensive, with fewer choices.

There are numerous antenna mounts available for nearly any situation. A NMO type antenna and mount will give you the most choices should you want or need to change to a different type of antenna in the future.

John
 

bharvey2

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Note to forum participants thinking of joining this thread:

Answer the OP's question about his antenna choices. Don't get wrapped around the axle about how the radio is being used.

To the OP, the radio you reference is designed for the amateur radio market. You don't mention that you or the other members of your group are licensed amateur radio operators. If they are, great! The Kenwood TM-281A is not designed to be used outside the amateur radio bands. If you transmit with the radio outside the amateur radio bands, you are violating FCC rules. If you transmit in the amateur radio bands without an amateur radio license, you are violating FCC rules.
But, but... (Before I finished reading his post I figured he was going to get hammered with the rules)

Okay, all funning aside, since you probably won't be able to come up with much of a ground plane, this might be a good option. A 1/2 wave, wide band, mobile antenna that can be tuned to 2M. You'd still need a base for mounting: https://www.tessco.com/products/displayProductInfo.do?sku=345727
 

kayn1n32008

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Hello everyone. Brand new to the forum and radios in general. I'll give a little background about my situation before I ask questions. I live in WV and ride my utv (Polaris General) in some VERY rural locations. The group I ride with uses VHF radios for comms. Quite a few use the Kenwood model listed above and that's the radio I've decided to purchase as well. I want to maximize my range as best I can with the best antenna options available. We ride in some pretty round conditions though. Creeks, mud, heavy brush and trees, heavy snow etc. Most of the body is plastic, so a magnet mount antenna won't work. I'll have to chassis mount it somewhere. So.... questions:

1: Would a 6' - 8' steel whip work with these radios? What's the longest length I can use? I have a specific reason for wanting to use a whip, if possible.

2: Could I use a spring at the base of an antenna to alleviate stress on it.

3: Would a dual antenna setup improve anything?

4: What antennas would you recommend for my situation?

I'm sure these questions may sound a little juvenile. I have very little experience with radios so any knowledge or info shared would be GREATLY appreciated. Thanks in advance.

Neil
Hi Neil

1: A 6-8 foot antenna will not work.

2 Yes you can put a spring on the coil to reduce stress on the whip/coil/mount.

3: Dual antennas will not help any.

4: Because you are using a UTV and there is not much metal in the roof, my recommendation would be a Laird or Larsen 1/2 wave antenna. I am partial to Larsen, I have used Larsen for many, many years, 6 years I have had them on various work trucks in the Alberta oilpatch, they are not treated the nicest, and I have not had one fail yet.

Not sure on the Laird part number but the Larsen is called a 'NMO-WB' there are various options for colour and spring/no spring.

As far as tuning, the Larsen is pretty wideband. If you cut it for 162MHz, it will give you an acceptable match from 150-174MHz. in addition, you will want to buy an NMO mount to suit your particular vehicle.
 

902

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Hello everyone. Brand new to the forum and radios in general. I'll give a little background about my situation before I ask questions. I live in WV and ride my utv (Polaris General) in some VERY rural locations. The group I ride with uses VHF radios for comms. Quite a few use the Kenwood model listed above and that's the radio I've decided to purchase as well. I want to maximize my range as best I can with the best antenna options available. We ride in some pretty round conditions though. Creeks, mud, heavy brush and trees, heavy snow etc. Most of the body is plastic, so a magnet mount antenna won't work. I'll have to chassis mount it somewhere. So.... questions:

1: Would a 6' - 8' steel whip work with these radios? What's the longest length I can use? I have a specific reason for wanting to use a whip, if possible.

2: Could I use a spring at the base of an antenna to alleviate stress on it.

3: Would a dual antenna setup improve anything?

4: What antennas would you recommend for my situation?

I'm sure these questions may sound a little juvenile. I have very little experience with radios so any knowledge or info shared would be GREATLY appreciated. Thanks in advance.

Neil
Hi Neil, and welcome to RR.

1. Yes, but no. The way radio works, longer isn't necessarily better. You want "resonant." See, longer will work worse if it's not resonant to the right frequency. N4GIX gave those dimensions. For VHF, getting your antenna higher on the vehicle would make it work much better than having a longer antenna.

2. Sure. But if you cut your antenna to about 18" to make it resonant to a "quarter wave," you might not need the spring.

3. Probably not. If you're thinking about one antenna on each side of the vehicle with a harness in between them, like the truckers use on CB, what happens there is instead of getting a nice, round "radiation pattern," you get what looks like a figure-8. That works great up and down the highway, but if you're off to the side, not so much.

4. I would recommend a 5/8 wave antenna on a base plate that has a 3/4" hole drilled in it. I'd weld that base plate to the rollbar. That's just me. The rollbar would be the "groundplane." I like the suggestions of a half-wave antenna pretty good, too.
 

jwt873

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The group I ride with uses VHF radios for comms. Quite a few use the Kenwood model listed above and that's the radio I've decided to purchase as well.l
What antennas do they use? You're best bet is to duplicate what they've done antenna-wise as far as mounting etc.. Plus they'll be able to tell you where they purchased the equipment.
 

mmckenna

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Good advice above.

I'm running a similar setup/different radio.
I've got a 2010 Polaris Ranger and I ride in similar conditions. Either far Northern California, or far Eastern California/Western Nevada. Lots of trees, mountains, canyons, hills, water crossings, snow, mud, etc. etc....

I've tried a number of different antennas on the Polaris Ranger and my dad and brothers Polaris Rzrs.
1/4 wave VHF antennas (about 19" tall) will work, but they rely on a ground plane under the antenna. This needs to be a metal surface, preferably 19 inches in all directions. This is entirely do-able on a UTV, but you'll need to have a roof. Mounting the antenna through the center of the roof will give you a proper ground plane under the antenna. The proper ground plane will keep coverage equal in all directions. When you offset the antenna on the ground plane, a situation where you may not have 19 inches in all directions, your antenna pattern will become lopsided and you may experience coverage deficiencies in certain directions.

Most mobile antennas require a ground plane, so going from that angle, you need to have a roof for it to work. Mounting one of these antenna on the roll cage will result in an unequal ground plane.

There is an option, though...
A half wave antenna does not require a ground plane (although it works better with one). A half wave antenna can be mounted just about anywhere and work.

After trying 1/4 wave and 5/8th's wave antennas on my Polaris, I finally tried a half wave. It works very well and seems to outperform the others.
Being that it doesn't require a ground plane, I can mount it off set to one side on the top of the roll cage.



This has worked well and it's taken quite a beating. Rough trails, tree branches, being on a flat bed trailer at highway speeds, etc. and no issues.

A couple of things to consider.
- Ideally, you do want to put the antenna in the center of the roll cage. Do this if you can. I didn't for various reasons, but it still works as is.
- RF radiation exposure at the power levels your radio runs at isn't trivial. While it's not going to give you cancer (right away) it's not considered safe by any reputable agency. Ideally you do want a couple of feet between your head and the antenna. Since your head is not easily relocatable, you may want to think about where you mount the antenna.
-You absolutely do want the antenna up as high as you can get it. Top of the roll cage is the way to go. Placing it anywhere else is going to result in decreased performance.
-You do want the spring base. While the whips will take a fair amount of abuse, mine has a slight kink in the very end. The spring probably has prevented me having to replace the whip. Hitting a tree branch at fast trail speeds is going to happen, so plan for it.
-I ran a roof on my Polaris for a while. I disliked it and removed it after a few years. The aluminum or steel roof tops are good for mounting antennas, but it's up to you. Ideal place would be to mount the antenna on the roof.
-You need to have a solid mount. Vibration and tree branch strikes will let you know quickly if your mount is not up to the task. There are some ready made mounts that will fit the roll cage pipe diameters. They work well.
-Make sure you -carefully- route the coax cable. Anywhere it's exposed to trail debris, rocks, mud, etc. is going to be an issue. Secure it along the back of the roll cage if possible. Routing it to the radio is going to take some thought. Remember that those rocks flying off the tires are going fast and -will- damage the coaxial cable. For this reason, inspect it often.

Some might try to steer you towards the higher gain antennas. 5/8th's waves and larger do provide some additional gain, which can make it act like your radio is running more power than it really is, but this comes at a cost. Gain antennas work by focusing the radiated power out towards the horizon. This is great if you are riding flat trails out on the plains, but you aren't. And I"m not. Lower gain works better. When on off camber trails, climbing/descending hills, etc. the tight pattern of the higher gain antennas can send more of your RF power towards the sky and ground. Don't fall into the trap of wanting more radiated power by using high gain antennas. In this instance it will work against you.

A few other items to consider:
Route the power for the radio directly off the battery. The ignition systems on some of the engines can be a bit noisy. Tapping into existing wiring can introduce a lot of noise into your radio. You do not want this.
An external speaker is really a good idea. The smallish speakers on these radios are fine inside a quite car, but they are useless when running down the trail at 40+mph. If you wear a helmet, you'll have a hell of a time hearing radio traffic. I'm running a large external Motorola speaker on my VHF radio in the Polaris. Running flat out on a trail (50+mph) with a full face helmet on I can still clearly hear the radio.
Careful where you mount the radio and speaker. It -will- get wet, muddy, snowed on, rained on, etc. Mine is under the dash board. Actually, I'm running a Motorola CDM-750 VHF. The actual radio guts are inside the glove compartment. The only thing exposed to the outside is the radio control head, well under the dash, and the speaker, also under the dash. So far, no issues.

Vibration is a real issue. Make sure your radio is well secured. Mine is bolted through the plastic under the dash and through an aluminum bar I installed to spread out the weight. Don't rely on things like double sided tape or sheet metal screws. They won't last.
Secure all the wiring well. Make sure vibration won't knock anything loose. My power connection at the battery is done with crimped ring terminals. The terminals are fully crimped, a touch of solder added, and then followed up with marine grade heat shrink. About 2K miles on the Polaris and no issues.

For the antenna mount:
I fabricated my own using this bracket as a starting point. Make sure the mount you purchase fits the diameter of your roll bar. Different brands use different diameter roll bars!
https://www.rockymountainatvmc.com/p/1430/25100/Tusk-UTV-Horizontal-Flag-Mount?term=roll+cage+antenna+mount

For the antenna base:
You'll want an NMO type base. You can find these online from several sources. Use a brand name mount, NOT Tram or Browning. These two brands (actually the same company) are mass produced in China and have questionable quality. Go with Larsen, Comtelco, Laird, antenex.... The NMO mount is a standard size, so the NMO mount from one brand will fit the antennas from another -in most cases-.

For the coaxial cable:
This will usually come as part of the NMO antenna base. Make sure you get the correct connector on the end. Your radio requires a Male "UHF" type mount, also called a PL-259. If you have not installed coaxial connectors before like these, buy the mount with the connector already installed. Try to NOT use adapters if at all possible. These create a failure point.

For the antenna:
Something like this will work just fine:
PCTEL | VHF Base Loaded Chrome Coil Antennas, No Ground Plane | MHB5802(S)

A lot of these parts you can get from ruggedradios.com They tend to be quite expensive though. Shopping around will get you a better price (easily). If you have any specific questions, post back here and we can assist.
 
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